JPS5851380B2 - television image projection device - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a device for projecting a television image projected on a cathode ray tube onto a projection screen and projecting the image in a large size, with the aim of making the brightness uniform and improving the contrast. It is.

First, there are several types of devices that use cathode ray tubes to project color television images onto a screen.

Typical such projection devices are shown and explained in FIGS. 1 to 3.

In the system shown in FIG. 1, a color television image is projected onto a projection screen 3 by a projector consisting of a single color cathode ray tube 1 and a single projection lens system 2 (usually including a plurality of lenses). It is something that is projected.

The one shown in FIG. 2 uses a projector consisting of three cathode ray tubes 4 that emit monochromatic images of red, green, and blue, and three projection lens systems 5 installed in each of the cathode ray tubes 4. Each monochromatic television image is projected onto the projection screen 3 and combined on the projection screen 3 to project a color television image.

The one shown in Figure 3 uses a Schmidt optical system instead of a projection lens system to project small-diameter red, green,
A projector consisting of a cathode ray tube 6 that emits blue monochromatic images, three spherical reflecting mirrors 7 and a Schmidt optical correction plate 8 installed on each cathode ray tube 6 displays each monochromatic television image on the projection screen 3. are projected and combined on the projection screen 3 to project a color television image.

All of these systems have a common structure consisting of a cathode ray tube for projection, a projection optical system, and a projection screen. There is insufficient light in the surrounding area,
In addition, there is a problem in that the contrast in the central portion is reduced, making it impossible to obtain a good image.

This phenomenon becomes more pronounced as the projection becomes wider, but for example, in terms of brightness, when projecting onto a 50-inch projection screen 3 using a relatively excellent optical system, the brightness at the center of the projection screen 3 may be reduced. According to actual measurements, if it is 100, it becomes about 70 near the top and bottom ends, about 50 near the left and right ends, and about 33 near the four corners.

However, at this time, the angle from the projector to the width of the projection screen 3 is approximately 37 degrees.

On the other hand, regarding contrast, in general, in a projection optical system, reflected light due to halation, stray light, or external light from the side of the projection screen tends to concentrate in the center of the image plane of the cathode ray tube. This overlaps with the image on the projection screen 3 and lowers the contrast at the center of the image on the projection screen 3.

Therefore, although cathode ray tubes usually have uniform emission brightness, the amount of light in the peripheral area of the projection optical system is reduced.
A process in which the image output signal is modulated in both the horizontal and vertical directions with parabolic or similar waveforms to reduce the brightness near the center of the fluorescent surface of the cathode ray tube, or in which the image light rays pass through the projection optical system or projection screen. In this case, it is also possible to try to obtain a uniform brightness distribution on the projection screen 3 by reducing the amount of light in a portion corresponding to the center of the image on the projection screen 3 and lowering the brightness in that center. However, these methods have the disadvantage that although the brightness can be made almost uniform, the contrast cannot be improved.

In view of these conventional drawbacks, the present invention makes the brightness of the television image projected on the projection screen uniform in both the center and the periphery, prevents the above-mentioned decrease in contrast in the center, and improves the brightness over the entire surface. An object of the present invention is to provide a device capable of projecting a television image with a high contrast.

In order to achieve this object, the present invention absorbs a portion of the light of the television image emitted from the image surface of the cathode ray tube that projects the television image to be projected, and also absorbs the light incident on the image surface. An absorbing substance that has a black color to be absorbed or a color that is complementary to the color emitted by the cathode ray tube,
The feature is that the amount of light projected from the image surface is lowered at the periphery of the image surface and increases toward the center, so that the amount of light projected from the image surface is lowered at the center than at the periphery of the image surface. By reducing the brightness, the brightness is made uniform over the entire surface, and in addition, in the center of the image plane, the reflectance of the back incident light is reduced by absorbing the light that is incident on the center of the image plane due to external light etc. with an absorbing material. This aims to improve the contrast in the central area.

Embodiments of the present invention will be described in detail below with reference to the drawings.

First, FIG. 4 shows an embodiment in which the amount of projected light of the fluorescent surface 10 itself on the image plane of the east cathode ray tube 9 is made larger toward the center and smaller toward the center relative to reverse incident light.

As a means for changing the amount of projected light and the reflectance, a particulate absorbing substance 11 such as a black pigment or a pigment of a color complementary to the emitted light color of the phosphor surface 100 is mixed into the phosphor 12 and the front glass 13 is changed. The simplest and most effective method is to apply the absorbent material 11 to the inner surface, and to make the amount of the absorbent material 11 smaller at the periphery and larger toward the center.

This measure is particularly advantageous for monochromatic cathode ray tubes.

In FIG. 5, the fluorescent surface 10 is assumed to emit light uniformly as in the conventional case, and the absorption rate of the projected light on the front glass 13 of the cathode ray tube 9 is set to be small at the periphery and increase toward the center, and vice versa. This is an embodiment in which the reflectance for incident light is increased toward the center.

Changes in absorption and reflectance in this case can be achieved by mixing the same absorbing substance 11 as described above in the front glass 13 itself, less at the periphery and more at the center, or by 130 surface or back surface may be coated with absorbing material in a similar distribution.

Further, in FIG. 6, the fluorescent surface 10 and the front glass 13 are made to emit light uniformly and reflect uniformly as in the conventional case, and the absorption rate of the projected light immediately before the front glass 13 is large in the center and small in the periphery. , an auxiliary transparent plate 14 is provided whose reflectance for reversely incident light is small at the periphery and increases toward the center.

As the auxiliary transparent plate 14, a transparent resin film mixed with or coated with the absorbing substance 11 in the same manner as above is used such that it is less in the periphery and more in the center, or For example, a transparent photographic film that becomes darker toward the center may be used.

The embodiments shown in FIGS. 5 and 6 can be applied to monochromatic cathode ray tubes as well as non-monochromatic cathode ray tubes.

Of course, it goes without saying that the above reflectance may be achieved by any other means.

In this way, by making the absorption rate of the projected light from the image plane of the cathode ray tube 9 smaller at the periphery and larger toward the center using the absorbing material, it is possible to reduce the absorption rate from the image plane of the cathode ray tube 9 to the projection screen 3. The brightness of the image projected on the projection screen 3 can be made smaller toward the center, making the brightness of the television image on the projection screen 3 the same in both the periphery and the center, resulting in a television with uniform brightness throughout. Images can be projected.

In addition, regarding contrast, even if reflected light or stray light due to annulation in the optical system, or light incident reversely from the projection screen side enters the center of the image plane of the cathode ray tube 6, this reverse incident will occur. Since the incoming light is absorbed by the absorbing material and its reflectance is reduced in the center, this prevents the re-reflection of these reversely incident lights and prevents a decrease in image contrast due to the re-reflected light. This means that an excellent television image with good contrast can be projected onto the projection screen 3.

In particular, such a projection optical system uses a lens system or a reflecting mirror system, so reflected light or stray light during projection or incident light from outside the projection system is absorbed by the lens system or reflecting mirror system. Due to the principle of retrograde light rays and the light condensing effect, the light is often incident backwards so that it reaches more of the center of the image plane.

Therefore, if a large amount of absorbing material is placed in the center of the image plane, as in this device, to absorb more of the back incident light and reduce the reflectance, the decrease in contrast in the center of the screen can be prevented. This can be most effectively prevented and the effect of improving contrast can be increased.

As described in detail above, according to the present invention, the color is black, which partially absorbs the light of the television image emitted from the screen and also absorbs the light incident on the screen, or has a complementary color relationship with the emitted color of the cathode ray tube. It is characterized by the fact that an absorbing substance having a certain color is provided on the image plane or in front of it so that it is less at the periphery of the image plane and more towards the center, so that the brightness of the projected television image can be reduced. It is possible to make the periphery and the center uniform, and also to prevent a decrease in contrast due to reverse incident light in the center, making it possible to project an excellent television image with good contrast over the entire surface. It is something.

Furthermore, if this absorbing substance is mixed into the phosphor of a cathode ray tube, it can be easily realized, especially in the case of monochromatic emission. If an auxiliary transparent plate is provided just in front of the front glass and an absorbing material is mixed or coated on this auxiliary front plate, it can also be applied to cathode ray tubes that do not emit monochromatic light.

[Brief explanation of the drawing]

1, 2, and 3 are schematic cross-sectional views for explaining the basic system of a television image projection device, and FIGS. 4, 5, and 6 are televisions according to different embodiments of the present invention. FIG. 2 is a cross-sectional view of main parts of the image projection device. 1.4,6...Cathode ray tube, 2,5...
Projection lens system, 3... Projection screen, 7...
...Reflector, 8... Schmidt optical correction plate, 9... Cathode ray tube, 10... Fluorescent surface, 1
1... Absorbing substance, 12... Fluorescent material, 13
...Front glass, 14...Auxiliary transparent plate.

Claims (1)

[Claims] 1. A cathode ray tube that projects television images onto a screen;
It is equipped with an optical system such as a projection lens that projects the television image on the image plane of the cathode ray tube onto a projection screen, and absorbs a part of the light of the television image emitted from the image plane and also absorbs the light that is incident on the image plane. An absorbing substance having a black color or a color complementary to the emission color of the cathode ray tube, which absorbs the light emitted by the cathode ray tube, is provided on the image plane or in front thereof such that it decreases at the periphery of the image plane and increases toward the center. A television image projection device characterized by: 2. The television image projection device according to claim 1, wherein an absorbing substance is mixed into the phosphor of the cathode ray tube. 3. The television image projection device according to claim 1, wherein an absorbing substance is mixed or coated on the front glass of the cathode ray tube. 4. The television image projection device according to claim 1, characterized in that an auxiliary transparent plate is provided in front of the front glass of the cathode ray tube, and an absorbing substance is mixed or coated on the auxiliary front plate.